Homeland Security Secretary Janet Napolitano's outgoing communications chief is known for his combative style. But in a confrontation that was undisclosed until now, he once threatened to "f---ing decapitate" the staff at the immigration office press shop.

The email outburst from Assistant Secretary for Public Affairs Sean Smith so startled one of the employees on the receiving end that she made an internal complaint against him. She described the threat as "serious misconduct" and requested a "full investigation" from the Office of Inspector General.

Emails obtained by FoxNews.com depict the exchange, which started when Smith criticized the immigration press team in response to a suspected leak. As Smith prepares to leave the department this month, Kelly Nantel, the employee who filed the complaint in late 2009, expressed concern that it was never fully addressed.

Nantel confirmed to FoxNews.com that she "took action" in response to the emails.

"I took what I thought was appropriate action," she said. Nantel was lead press secretary at Immigration and Customs Enforcement at the time; she recently left to work for the National Transportation Safety Board.

Department of Homeland Security spokeswoman Amy Kudwa said the complaint was passed on from the inspector general to the Office of the General Counsel, which conducted an inquiry and apparently did not consider the email a bona fide threat.

"After conducting a thorough review, (the agency) determined that, although the email was inappropriate, the email did not constitute a legitimate threat to Ms. Nantel," Kudwa said in a written statement. "Mr. Smith was counseled by senior departmental leaders and apologized to Ms. Nantel. They worked together amicably until she departed ICE for a position at the NTSB earlier this year."

Nantel, though, said she was "unaware that it was ever resolved."

The confrontation in August 2009 flared after an Associated Press reporter sent an email to the Homeland Security press staff asking about an upcoming detention center announcement -- a story DHS was already coordinating with The New York Times on. The reporter was apparently tipped off to the news, raising questions about the possibility of a leak.

After some back-and-forth among the staff, Smith sent an email to Nantel and her deputy Richard Rocha with the following:

"I swear to f---ing god I am going to come over to ICE and f---cking decapitate every single person in both the press shop and leg shop," he wrote. "Not only does Eileen have all this information, she also knows the NYT has it. Only 3-4 people knew that, and most of them are on this email chain."

He ended the note with, "John, we need to talk about the future of your press shop." The last part was directed toward John Morton, the director of ICE who was copied on the email along with a few other officials.

Smith evidently tried to make amends afterward. A day after he snapped at his staff via email, he sent a follow-up applauding the team for the coverage they ended up getting on the detention announcement.

"I also want to apologize for (the) email I sent yesterday," he wrote, explaining that "frustrations" with the AP's fact-finding got the better of him. "I'm sorry for saying such dumb things."

He told Nantel and Rocha that they've been "great partners."

But by that point, Nantel was already drafting her complaint, which she sent. Nantel wrote in the email that she felt "compelled" to file it in accordance with official policy and her duties as a supervisor.

She then informed Smith, telling him that while she acknowledged his "apology," his email "was wholly inappropriate and unprofessional."

"You not only attacked my professional credibility, but that of my staff without any factual information," Nantel wrote, adding that "threats against me and my staff" should not go unaddressed.

Internal emails show a handful of exchanges about her complaint following the incident. In one email sent the following week, Nantel was informed that a lawyer with the Office of the General Counsel had been assigned to "conduct the review." Nantel followed up a month later, asking another official for an "update" on the review -- she noted that "we are still under the prohibition from dealing directly with Sean." Nantel was told to expect to "hear something soon."

Nearly two weeks later, Nantel asked again, and was told "they are not helping us out."

It is unclear what other conversations took place among investigators. Kudwa described the inquiry as thorough.

Smith came to Homeland Security from the campaign trail. He had been working as the Obama campaign's Pennsylvania communications director in 2008. Before that, he worked for Sen. Joe Lieberman's 2006 re-election campaign.

Smith, as Lieberman's campaign manager in the dramatic primary battle against Democrat Ned Lamont, made waves in 2006 when he accused political opponents of sabotaging Lieberman's campaign website and email. He described the apparent service disruption as a "coordinated attack," and the campaign notified state and federal investigators of the allegation.

However, nearly two years later, the local Stamford Advocate newspaper reported on an FBI email that said investigators found no evidence of an attack, and that the website was just poorly configured.

Smith, after moving on to the Obama campaign, eventually secured the high-ranking position within the Obama administration. Nantel, by contrast, is a career employee originally hired during the prior administration.